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Changes in the Size of the Active Microbial Pool Explain Short-Term Soil Respiratory Responses to Temperature and Moisture.

Salazar-Villegas A, Blagodatskaya E, Dukes JS - Front Microbiol (2016)

Bottom Line: Most current approaches to model microbial control over soil CO2 production relate responses to total microbial biomass (TMB) and do not differentiate between microorganisms in active and dormant physiological states.TMB responded very little to short-term changes in temperature and soil moisture and did not explain differences in SBR among the treatments.These results suggest that decomposition models that explicitly represent microbial carbon pools should take into account the active microbial pool, and researchers should be cautious in comparing modeled microbial pool sizes with measurements of TMB.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Purdue UniversityWest Lafayette, IN, USA; Purdue Climate Change Research Center, Purdue UniversityWest Lafayette, IN, USA.

ABSTRACT
Heterotrophic respiration contributes a substantial fraction of the carbon flux from soil to atmosphere, and responds strongly to environmental conditions. However, the mechanisms through which short-term changes in environmental conditions affect microbial respiration still remain unclear. Microorganisms cope with adverse environmental conditions by transitioning into and out of dormancy, a state in which they minimize rates of metabolism and respiration. These transitions are poorly characterized in soil and are generally omitted from decomposition models. Most current approaches to model microbial control over soil CO2 production relate responses to total microbial biomass (TMB) and do not differentiate between microorganisms in active and dormant physiological states. Indeed, few data for active microbial biomass (AMB) exist with which to compare model output. Here, we tested the hypothesis that differences in soil microbial respiration rates across various environmental conditions are more closely related to differences in AMB (e.g., due to activation of dormant microorganisms) than in TMB. We measured basal respiration (SBR) of soil incubated for a week at two temperatures (24 and 33°C) and two moisture levels (10 and 20% soil dry weight [SDW]), and then determined TMB, AMB, microbial specific growth rate, and the lag time before microbial growth (t lag ) using the Substrate-Induced Growth Response (SIGR) method. As expected, SBR was more strongly correlated with AMB than with TMB. This relationship indicated that each g active biomass C contributed ~0.04 g CO2-C h(-1) of SBR. TMB responded very little to short-term changes in temperature and soil moisture and did not explain differences in SBR among the treatments. Maximum specific growth rate did not respond to environmental conditions, suggesting that the dominant microbial populations remained similar. However, warmer temperatures and increased soil moisture both reduced t lag , indicating that favorable abiotic conditions activated soil microorganisms. We conclude that soil respiratory responses to short-term changes in environmental conditions are better explained by changes in AMB than in TMB. These results suggest that decomposition models that explicitly represent microbial carbon pools should take into account the active microbial pool, and researchers should be cautious in comparing modeled microbial pool sizes with measurements of TMB.

No MeSH data available.


Related in: MedlinePlus

Contributions of temperature, soil moisture, and their interactions to the variance of soil basal respiration, total microbial biomass, active microbial biomass, μ, and tlag, measured as described in Section Statistical Analysis and Curve Fitting. T, Temperature; SM, Soil moisture.
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Figure 6: Contributions of temperature, soil moisture, and their interactions to the variance of soil basal respiration, total microbial biomass, active microbial biomass, μ, and tlag, measured as described in Section Statistical Analysis and Curve Fitting. T, Temperature; SM, Soil moisture.

Mentions: Temperature typically explained more of the variation in soil microbial parameters (especially AMB and tlag) than did soil moisture (Figure 6). However, both environmental factors were important in explaining variation in SBR, and the two together accounted for 70% of this variation. This analysis accounts for the direct effects of temperature and moisture on SBR (e.g., 29% of variance explained by temperature) and microbial parameters (e.g., 59% of variance in AMB explained by temperature). In contrast, the relationships between SBR and microbial biomass (Figure 5) suggest that microbial activation was the biological mechanism through which these abiotic factors influenced soil respiration rates (e.g., 62% of the variance in SBR was explained by environmentally—mainly temperature—driven changes in the pool of AMB).


Changes in the Size of the Active Microbial Pool Explain Short-Term Soil Respiratory Responses to Temperature and Moisture.

Salazar-Villegas A, Blagodatskaya E, Dukes JS - Front Microbiol (2016)

Contributions of temperature, soil moisture, and their interactions to the variance of soil basal respiration, total microbial biomass, active microbial biomass, μ, and tlag, measured as described in Section Statistical Analysis and Curve Fitting. T, Temperature; SM, Soil moisture.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4836035&req=5

Figure 6: Contributions of temperature, soil moisture, and their interactions to the variance of soil basal respiration, total microbial biomass, active microbial biomass, μ, and tlag, measured as described in Section Statistical Analysis and Curve Fitting. T, Temperature; SM, Soil moisture.
Mentions: Temperature typically explained more of the variation in soil microbial parameters (especially AMB and tlag) than did soil moisture (Figure 6). However, both environmental factors were important in explaining variation in SBR, and the two together accounted for 70% of this variation. This analysis accounts for the direct effects of temperature and moisture on SBR (e.g., 29% of variance explained by temperature) and microbial parameters (e.g., 59% of variance in AMB explained by temperature). In contrast, the relationships between SBR and microbial biomass (Figure 5) suggest that microbial activation was the biological mechanism through which these abiotic factors influenced soil respiration rates (e.g., 62% of the variance in SBR was explained by environmentally—mainly temperature—driven changes in the pool of AMB).

Bottom Line: Most current approaches to model microbial control over soil CO2 production relate responses to total microbial biomass (TMB) and do not differentiate between microorganisms in active and dormant physiological states.TMB responded very little to short-term changes in temperature and soil moisture and did not explain differences in SBR among the treatments.These results suggest that decomposition models that explicitly represent microbial carbon pools should take into account the active microbial pool, and researchers should be cautious in comparing modeled microbial pool sizes with measurements of TMB.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Purdue UniversityWest Lafayette, IN, USA; Purdue Climate Change Research Center, Purdue UniversityWest Lafayette, IN, USA.

ABSTRACT
Heterotrophic respiration contributes a substantial fraction of the carbon flux from soil to atmosphere, and responds strongly to environmental conditions. However, the mechanisms through which short-term changes in environmental conditions affect microbial respiration still remain unclear. Microorganisms cope with adverse environmental conditions by transitioning into and out of dormancy, a state in which they minimize rates of metabolism and respiration. These transitions are poorly characterized in soil and are generally omitted from decomposition models. Most current approaches to model microbial control over soil CO2 production relate responses to total microbial biomass (TMB) and do not differentiate between microorganisms in active and dormant physiological states. Indeed, few data for active microbial biomass (AMB) exist with which to compare model output. Here, we tested the hypothesis that differences in soil microbial respiration rates across various environmental conditions are more closely related to differences in AMB (e.g., due to activation of dormant microorganisms) than in TMB. We measured basal respiration (SBR) of soil incubated for a week at two temperatures (24 and 33°C) and two moisture levels (10 and 20% soil dry weight [SDW]), and then determined TMB, AMB, microbial specific growth rate, and the lag time before microbial growth (t lag ) using the Substrate-Induced Growth Response (SIGR) method. As expected, SBR was more strongly correlated with AMB than with TMB. This relationship indicated that each g active biomass C contributed ~0.04 g CO2-C h(-1) of SBR. TMB responded very little to short-term changes in temperature and soil moisture and did not explain differences in SBR among the treatments. Maximum specific growth rate did not respond to environmental conditions, suggesting that the dominant microbial populations remained similar. However, warmer temperatures and increased soil moisture both reduced t lag , indicating that favorable abiotic conditions activated soil microorganisms. We conclude that soil respiratory responses to short-term changes in environmental conditions are better explained by changes in AMB than in TMB. These results suggest that decomposition models that explicitly represent microbial carbon pools should take into account the active microbial pool, and researchers should be cautious in comparing modeled microbial pool sizes with measurements of TMB.

No MeSH data available.


Related in: MedlinePlus